Background: Diagnosis of pancreatic cancer (PC) in early stages is still challenging for gastroenterologists. The early detection of cancer is one of the utmost importance for the successful therapy of this malignancy. An accurate differential diagnosis of focal pancreatic lesions plays also an important role, whether it is differential diagnosis of chronic pancreatitis from PC or autoimmune pancreatitis (AIP) from PC. Raised serum immunoglobulin G4 (IgG4) levels to twice the normal value are considered one of significant diagnostic features of type 1 AIP. However, IgG4 can be increased also in patients with PC, but levels usually do not exceed twice the normal value. Methods: In years 2012-2017, IgG4 serum levels were examined in 115 patients with histologically confirmed PC. Patients with PC and elevated IgG4 level (above 135 mg/dL) had tested their histological resection specimens or bioptic specimens from pancreatic lesion, with targeted detection of the presence of IgG4 and plasmocytes in the pancreatic tissue and changes characteristic for type 1 AIP. Results: A plasmatic IgG4 level in 115 patients with diagnosed PC was higher than 135 mg/dL in 14 patients (12.2%). Out of them, 2 patients (1.7%) revealed a serum IgG4 level higher than double the normal value, that is, higher than 270.0 mg/dL (suggestive of AIP). One patient met histological criteria for diagnosis of AIP in the simultaneous presence of PC. Conclusion: Diagnosis of early cancer stages, particularly differentiating AIP from PC can be sometimes problematic. IgG4 levels can be slightly elevated also in case of PC. A targeted biopsy of the pancreas is the method of choice in cases suspected from a focal form of AIP and we recommend to prefer it over other modalities, such as, for example, response to steroid therapy. (c) 2019 S. Karger AG, Basel